The present invention is generally related to telephone keypads and more particularly to an improved low-profile, rubber keypad for use in cellular portable telephones.
Prior art low-profile keypads are available that have good tactile feedback but typically do not allow back illumination through the interconnect and switching circuitry. In order to provide for back illumination and good tactile feedback, a high-profile keypad incorporating plunger type actuator keys or self-tactile rubber keypads is required. Back illumination through such high-profile keypads is not possible since the keys incorporate a carbon conductor or a metallic popple, both of which are opaque. This problem has been solved in part by using a separate lightpipe (see U.S. Pat. No. 4,124,879) or a thick rubber pad as a lightpipe (see U.S. Pat. No. 4,636,593) to distribute the required illumination to the keys of the keypad. For the foregoing reasons, there is a need for an improved low-profile keypad that has good tactile feedback and back illuminability.